Attenuator for surface wave propagation



Feb.ll9, 1957 A. G. CLAVIER Erm. 2,782,382

ATTENUATOR FOR SURFACE WAVE PROPAGATION Filed May 25, 1950 i.\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\` H v/ INVENTORS ANDRE VIER HOMAS CLA 0A VID L ATTORNEY United States Patent O ATTENUATOR FOR SURFACE WAVE PROPAGATION Andre G. Clavier, Nutley, N. J., and David L. Thomas,

Lee, London, England, assignors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application May 25, 1950, Serial No. 164,245

12 Claims. (Cl. S33-81) This invention relates to microwave transmission systems employing surface wave propagation and more particularly to attenuators for such systems.

In our copending application, Serial No. 163,581, filed May 23, 1950, we disclose various forms of guide lines together with associ-ated launching and receiving devices for surface wave propagation of microwave energy. The guide line may comprise either a bare conductor having a finite resistivity or a conductor with dielectric material distributed -therealong, either as -a continuous coating or as spaced sections or beads. The larger part of the electromagnetic field for such lines is confined in the form of a cylindrical volume closely adjacent the surface of the conductor thereby resulting in efiicient transmission of high frequency energy. By way of example, an ordinary No. l2 enameled copper wire has been found, for transmission of a high frequency energy, to have the major portion of the electromagnetic field concentrated within a 3 to 4 inch radius about the wire, and that the high frequency energy fiowed in this field along the surface of the wire with very low loss.

One of the objects of lthis invention is to provide an attenuator for guide lines capable of surface wave trans mission; and a further object is to provide an iattenuator for such lines which is easily adjustable.

The Aattenu'ator according to our invention comprises a first section adapted to be disposed in series with the guide line, said section having a predetermined impedance characteristic, and a second section having an impedance characteristic substantially different from the impedance characteristic of said first section, one of the sections being adjustable relative to the other to determine the impedance of the combined sections. More particularly, the attenuator, preferably in the form of a conductor line section *and ya surrounding dielectric member is adapted to be coupled to the guide line; the conductor line section being connected directly to the guide line and supported by insulator spacers which may be tapered down substantially to the surface of the guide line for matching purposes. A liquid dielectric having a dielectric coefiicient similar to that of the insulator spacers is contained in the system between the inner and outer members.

One of the features of the invention is that the conductor line section is provided with a length greatly reduced in cross-sectional size for attenuation purposes. A second line section in the form of a sleeve is disposed in telescoping contact with a portion of the conductor adjacent the reduced length, one end of the sleeve being provided with contact fingers for sliding engagement with the reduced portion of the conductor.

Another feature of the invention is the means for adjusting the sleeve so as to vary the length of the reduced portion of the conductor. In one form, a body of magnetizable material, such as soft iron, is secured to the sleeve whereby a control solenoid may be provided eX- teriorly of the surrounding dielectric member to control the position of the sleeve. A spring may also be utilized to determine the positioning of the sleeve when the sole- 2,782,382 Patented Feb. 19, 1957 noid is de-energized. Another means for adjusting the movement of the sleeve is to secure it to the dielectric member and provide the dielectric member with means for manual movement relative to the conductor. In still another form the conductor is separated, one end portion being made hollow while the other end portion is reduced sharply in :cross-sectional size for attenuation purposes. A sleeve is provided on the reduced conductor portions for telescoping movement into the hollow end portion. By providing the hollow conductor with a slot, the sleeve may then be adjusted by means of a slider connected to the sleeve and projected through the slot.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is `a View in longitudinal section of one form of attenuator made in accordance with the principles of our invention;

Fig. 2 is a longitudinal sectional view of a modified form of attenuator; and

Fig. 3 is a fragmentary view in longitudinal section of still another form of attenu'ator.

Referring to Fig. l, the attenuator comprises a coaxial system (not to be confused with a coaxial electrical system) 1 consisting of an inner conductor Zand an outer member 3. The inner conductor is provided with two end portions 4 and 5 which may comprise the end portions of a guide line or they may comprise conductors which can be coupled by suitable means to a guide line. To provide for attenuatiomthe conductor 2 includes a central part 6 of a partly reduced cross-sectional size. This part is of a length necessary to provide the desired maximum attenuation. The outer member 3 is in the form of'a hollow cylinder preferably of dielectric material, the ends of which are supported on the conductor parts 4 and 5 by insulating spacer discs 7. In order to match the coaxial section with the guide line and thus avoid undue perturbation of the high frequency energy, the bodies of insulating material 7a :are provided at the ends of the coaxial system adjacent the discs 7, which bodies are tapered down to substantially the surface of the conductor parts 4 and 5 or to the surface of the insulating coatings carried thereby. The interior of the coaxial system is filled with 'dielectric fluid 8 which has a dielectric coeicient of similar magnitude to that of the solid dielectric in bodies 7 and 7a and that of which vthe outer member 3 is constructed.

The impedance of the attenuator is made adjustable by varying the effective length of the central part 6 of the conductor 2. This is accomplished by providing a sleeve 9 concentrically about the conductor parts 5 and 6, the sleeve being preferably of a cross-sectional size similar to that of the conductor part 5. As shown in Fig. l, the sleeve 9 is slightly larger than the conductor part 5 so that it may telescope thereover in sliding contact therewith. The opposite end of the sleeve 9 is tapered and provided with resilient fingers 10 to make sliding contact with the reduced conductor part 6. Disposed within the sleeve is an annular body of soft iron 11 keyed or otherwise secured in the sleeve. A helical spring 12 is disposed about the conductor 6 between the iron slug 11 and the end of conductor part 5. The spring serves to normally hold the sleeve in a position such that it overlies for a major portion of its length the reduced conductor part 6. A control solenoid 13 is disposed about the outer member 3 adjacent the location of the sleeve so that when the solenoid is energized it will attract the slug 11 and thereby cause the sleeve to move against the action of spring 12 therebyuncovering a portion of the conductor part 6. Thus when the solenoid` is unenergized, the sleeve 9 overlies for a major portion of the4 sleeve length the conductor part 6 thereby reducingthe effective length of. the part 6` to a predetermined minimum, and when the solenoid 13 is energized? the sleeve is moved to the right, as viewed in Fig. 1, thereby uncovering a length of the part 6 whereby a maximum attenuating length is provided. Thus by controlling the energization of the solenoid 13 the degree of' attenuation between two predetermined limits is obtainable.

ln Fig. 2, a modified version of the attenuator is shown whereby conductor 2 is provided with two parts 14 and 1S with a sharply reduced central part 16 similarly as in the case of the form shown in Fig. l. 1n this form, the conductorV 2 is shown to be bare although it may be provided with an insulating coating if desired up to the` coaxial. structure. An outer member 17 is supported by insulating spacers 18 which are provided with aliquid tight gland 19 for sliding engagement with the inner conductor parts 14 and 15. The spacers 1S are preferably tapered at their outer ends for matching purposes. The, interior of the coaxial structure is pro vided with a fiuid dielectric 2) which corresponds in dielectric coefiicient to that of the insulator' spacers 13 and that of member 17.

A sleeve 21 is provided with resilient Contact ngers 22 and 23 for sliding engagement with the large conductor pait 14 and the small conductor part 16, respectively. Inter-connecting the -sleeve 21 with the outer member 1-7 is a perforated insulating disc 24. The perforations 2S are provided to permit the flow of fiuid dielectric when the sleeve 21 is moved. The movement of the sleeve is accomplished by manually moving the outer member 17 relative to the conductor 2. In this way the effective length of the small attenuating conductor` 16 may be changed, the degree of attenuation being determined by the adjustable length of the sleeve 21.

In Fig. 3, the conductor and sleeve arrangement of the attenuator is quite different from the form shown inV Figs. l and 2. In this embodiment, the line conductor 27 is shown to be hollow at one end 2S. The central attenuating conductor part 29 is separate from the hollow end part 28 but is disposed axially thereof. An adjustment sleeve 3f) is of such size as to be received in telescoping fashion into hollow-end portion 28. The sleeve is also provided with sliding contact fingers 31 for engagement with the conductor part 29. The opposite end of the sleeve is provided with a tubular extension 32 of smaller dimension with a slider element 33 extending at right angles thereto through a slot 34 contained in the hollow conductor portion 2S, the slotted part being disposed beyond the end. of the outer member 35. By manipulating the slider 33 the sleeve Sti may be =ad justed-v so as to vary the effective length of the conductor 29. rIhe outer member 35 is supported on the hollow end conductor 28 and a corresponding solid conductor part 36 at the other end of the center conductor 29 by means of insulating spacers 37. T oprovide for improved matching additional dielectric material 38 is placed =ad jacent the spacers 37 and tapered down to the surface of the dielectric coated conductor 27. The interior of the coaxial structure may likewise be provided with a uid dielectric which isv prevented from leaking out the slot 3,4, by meansA of glands 39 and 40 disposed between thev hollow conductor 28 and the extension 32 of the sleeve and between the. interior of the sleeve extension 32 and the conductor 29.

In the three figures of the drawings7 it will be apparent that the sleeves 9, 21 and 30 each bear a different cross-sectional size relationship with respect to the coacting conductor parts 5, 14 and 28, respectively. The main feature of. the attenuator is to provide a length of highly attenuating wire such as the center conductorl parts 6,

4 16 and 29 and to vary the effective length of these parts by sleeves which have impedance characteristics considerably different from the impedance characteristics of parts 6, 16 and 29, and adapted to provide matching '.if'ith surface wire transmission along the guide line to which the attenuator is attached.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention, as set forth in the objects thereof and in the accompanying claims.

What we claim is:

l. Anl attenuator in combination with a single conductor guide line of the type capable of surface propagation of high frequency energy by means of an electromagnetic eld formed about the guide line, said guide line presenting a predetermined impedance to said energy comprising a first single line section connected to said guide line and presenting a higher impedance to said energy than said guideline, and a slidable line section having one end in slidablev engagement with said first line section and a portion in slidable engagement with said guide line and presenting substantially the same i111- pcdance to said energy as said guide line, whereby the electrical impedance of said attenuator may be varied by changing the effective lengths of said guide line and said first line section upon moving said slidable line section.

2. The attenuator according to claim l, wherein said slidablev line section is a sleeve member in telescoping engagement with said first line section and said guide line.

3. ln an attenuator according to claim 2, further including an outer-member of dielectric material surrounding said first and second line sections, a liquid dielectric filling the space between said sections and said outer dielectric member, and said sleeve being provided with control means to effect movement thereof from outside said outer dielectric member.

4. In an attenuator according to claim 3, wherein the control means includes a body of magnetizable material carried by said movable section, a spring to urge saidr movable section in one direction to a given position and a solenoid disposed on the outside of said outer member to magnetically force said magnetizable material in a direction counter to said spring to effect and control movement of said movable section.

5. In an attenuator according to claim 3, wherein said control means includes means connecting said sleeve to said outer member whereby movement of the outer member relative to said first section effects movement of said sleeve.

6. The attenuator according to claim l, wherein said first line section is of smaller cross-sectional size than said guide line, and said slidable line section is approximately of the same cross-sectional size as said guide line.

7. The attenuator according to claim 2, wherein said first line section is connected intermediate two guide line portions, means connecting one end of said first line section directly to one of said guide line portions, the other of said guide line portions being hollow, means mounting the opposite end of said first line section within the hollow space of said other guide line portion, and said sleeve member having one part telescoping into said hollow space and a second part telescoping over said first line section.

8. An attenuator according to claim 7, wherein said attenuator includes fluid tight glands spanning the spacebetween said first line section and said sleeve, and between said sleeve and said other guide line portion to seal off said hollow space.

9. In an attenuator according to claim 3, wherein said outer dielectric member is hollow for a given length thereof, said hollow portion being aligned axially with said first line section, and said hollow guide line portion is provided] with a slot therein, and wherein said control means includes an element passing through said slot and connected to said sleeve, whereby longitudinal movement on said element in said slot correspondingly moves said sleeve.

10. An attenuator according to claim l, wherein said slidable line section comprises a conductive sleeve disposed concentrically about said single conductor guide line and said first single line section further comprising means including a body of magnetizable material carried by said sleeve for .adjusting the position of said sleeve along said conductor, a spring to urge said sleeve in one direction to a given position, and a solenoid disposed outside of said 'line sections and concentric therewith for operating upon said magnetizable material to adjustably force said sleeve in a direction counter to said spring to effect and control movements of said sleeve.

l1. An attentuator according to claim 1, wherein said slidable line section comprises a conductive sleeve disposed concentrically about said single conductor guide 'line and said first single line section, further comprising a dielectric member surrounding said single conductor guide line slidable with respect thereto, and control means connecting said sleeve to said dielectric member, whereby movement of the dielectric member relative to said single conductor guide line eiects movement of said sleeve.

l2. An attenuator according to claim ll, wherein said attenuator includes bodies of insulating material closing the ends of said dielectric member, said bodies having liquid tight glands about said conductor and liquid dielectric contained in the space between the conductor and dielectric member.

References Cited in the le of this patent UNITED STATES PATENTS 1,912,794 Peterson June 6, 1933 2,187,014 Buschbeck Jan. 16, 1940 2,405,437 Leeds Aug. 6, 1946 2,407,847 Peterson Sept. 17, 1946 2,423,461 Meahl July 8, 1947 2,427,643 Collard Sept. 16, 1947 2,438,795 Wheeler Mar. 30, 1948 2,497,707 Wetherill Feb. 14, 1950 2,514,344 Slaymaker et a'l. July 4, 1950 2,525,554 Latimer Oct. l0, 1950 2,627,550 Rose Feb. 3, 1953 

